Trailer hitches are in wide use for towing many kinds of trailing vehicles, e.g., boat trailers, autos and the like, behind another vehicle. As used herein, the term "trailer" refers to any type of vehicle, whether or not capable of self-propulsion, which is to be towed or is under tow by another vehicle.
Most such hitches use a spherical ball attached to one of the vehicles and a hollow, hemispherical coupler attached to the other. To hitch the vehicles together, the ball and coupler are brought into precise alignment, the coupler lowered onto the ball and the coupler latching lever pressed into place. And such hitches are available in a wide variety of sizes and ratings (and corresponding hitch component weights) to suit a broad range of requirements.
A major disadvantage of conventional hitches is that they are rigid. That is, they are made in such a way that once mounted to the vehicle, the spherical ball is in a fixed position with respect to such vehicle. Similarly, the coupler is in a position which, at least laterally and axially, is fixed with respect to the vehicle on which it is mounted. As a consequence, the ball and coupler must be precisely vertically aligned before the coupler can be lowered onto the ball for hookup. This is not a particularly imposing task if the trailer is lightweight and/or if two people, a driver and an observer, participate in the task.
However, trailers are often very heavy and, frequently, hookup is desired to be made by a single person working alone. And trailer hitches are often employed by elderly retired persons who, even working in pairs, are physically unable to perform the heavy pulling and tugging required to make a hookup with a conventional hitch and a heavy trailer.
Thus, conventional hitches are distinctly disadvantageous for the elderly and/or for persons working alone.
Yet another disadvantage of conventional hitches relates to the fact that to achieve precise alignment of ball and coupler, the observer is virtually required to stand between the vehicles as the towing vehicle is backed toward the trailer. Of course, this may present some risk to the observer if the driver of the towing vehicle is not extremely careful.
Earlier patents depict efforts to resolve some of these concerns. For example, the hitch shown in U.S. Pat. No. 4,176,854 (Hill et al.) has a bottom plate and upper cover plate shaped like a truncated triangle. A bar-like coupling arm fits into and slides in the space lateral swinging movement and axial movement to align the ball and the ball-hitch receiver.
U.S. Pat. No. 3,169,028 (Scrivner) shows a hitch very similar to that shown in the Hill et al. patent. That is, it has a flat drawbar which moves axially and laterally between top and bottom plates. Axial movement is both made possible and limited by a pin-and-groove arrangement.
U.S. Pat. No. 3,437,355 (Jeffes) shows a coupling with a hollow outer member and an inner member having portions shaped like the gripping end of a ball bat. The inner member can move axially in the outer member and when partially or fully extended, can also move laterally and vertically.
The hitch shown in U.S. Pat. No. 4,125,272 (Putnam, Jr. et al.) has an arm which hooks to a hitch ball on a towing vehicle and a rectangular-section, tube-like slide which fits into a guide tube on a trailer. The arm and slide are connected together by a universal joint which permits the arm to move laterally and up/down with respect to the slide. When the slide is fully outwardly extended (in what the patent calls a "prehitch" arrangement), a spring-biased pin on the trailer tongue engages the rear end of the slide and prevents disconnection.
In using such hitch, prehitching is performed first. Then the towing vehicle is driven forward and the towed vehicle, then supported on its own caster wheel(s), is drawn to an approximately aligned position. The towing vehicle then backs for final alignment and connection. Final alignment is aided by a pair of angled lateral sides on the arm.
U.S. Pat. No. 4,606,549 (Williams, Jr.) shows a hitch, the elongate shank unit of which is attached to a trailer ball socket before the trailer and the towing vehicle are coupled together. A hollow, tube-like receiving unit is attached to the towing vehicle and has a funnel-like mouth. As the towing vehicle is backed, the extended, rounded end of the shank unit is guided by the mouth into the receiving unit for later locking.
The hitch shown in U.S. Pat. No. 4,759,564 (Williams, Jr.) is closely similar to that shown in the Williams, Jr. patent noted above. A modification is that the shank unit shown in the '564 patent has a pair of stop blocks limiting unit travel at a location where pin engagement holes in the shank unit and the receiving unit are aligned. In both of the Williams, Jr. patents, aligned attachment is by backing the towing vehicle rather than by hand manipulation.
The hitch shown in U.S. Pat. No. 4,515,387 (Schuck) has an outer housing formed of parallel top and bottom plates and flared sides. An inner housing slides inward and outward within the outer housing and like the arrangement of the Scrivner patent discussed above, sliding movement is both permitted and limited by a pin-and-groove arrangement. The Schuck patent suggests that the inner housing (and the tongue within it) can be swung from side to side for alignment only when the inner housing is drawn fully outward. So constructed, the Schuck hitch is capable of aligned connection only along an arc, not axially.
U.K. Patent Application GB 2 069 430 shows sighting rods for aligning a towing vehicle with a trailer.